1. Field of the Invention
The present invention relates to AV amplifiers, and more particularly, to an AV amplifier capable of selectively switching between a multichannel reproducing mode and a two-channel stereo reproducing mode.
2. Description of the Background Art
Recently, the popularity an AV amplifier which performs multichannel reproduction of images and sounds is rapidly increasing due to increasing demand of home theaters. This kind of AV amplifier performs the multichannel reproduction by decoding audio information (which is multichannel audio information encoded as two-channel audio information) obtained from various sources (such as a DVD, digital broadcast and so forth). On the other hand, demands for stereo reproduction with a single high-class speaker compatible with bi-amp and bi-wiring (hereinafter referred to as a bi-wiring speaker), in which sound quality is valued, are still great. It is a great burden in terms of price and space to buy and set an amplifier for a home theater and an amplifier for stereo reproduction separately. Therefore, the use of one AV amplifier to perform multichannel reproduction and also drive bi-wiring speakers in stereo has been implemented.
A method of driving a bi-wiring speaker by using a conventional multichannel AV amplifier will be described below, referring to a drawing. FIG. 14 is a block diagram showing a state in which the bi-wiring speakers are connected to the conventional AV amplifier. In FIG. 14, two-channel signals (in which multichannel (here, four-channel) information is encoded) obtained from a source which is not shown in the figure (such as a DVD, digital broadcast and so forth) are inputted from input terminals 1L and 1R and decoded as original four-channel signals by a decoder 2. A signal 3L for a L channel outputted from the decoder 2 is amplified by an amplifier 4A for the L channel and then inputted to a terminal HF for high-frequency and a terminal LF for low-frequency of a bi-wiring speaker 6L for the L channel in parallel. Similarly, a signal 3R for a R channel outputted from the decoder 2 is amplified by an amplifier 4C for the R channel and then inputted to a terminal HF for high-frequency and a terminal LF for low-frequency of a bi-wiring speaker 6R for the R channel in parallel. A signal 3C for a C channel (a center channel) outputted from the decoder 2 is amplified by an amplifier 4B for the C channel and then inputted to a center speaker 11. Also, a signal 3S for a S channel (a surround channel) outputted from the decoder 2 is amplified by an amplifier 4D for the S channel and then inputted to a surround speaker 12.
The conventional AV amplifier has a problem such that in the case where the bi-wiring speakers 6L and 6R are driven in a two-channel stereo reproducing mode by using the conventional AV amplifier as described in the above, only two amplifiers which are the amplifier 4A for the L channel and the amplifier 4C for the R channel are used as an amplifying circuit, therefore the bi-wiring speaker is substantially used in a normal mode in which the terminals HF for high-frequency and the terminals LF for low-frequency are short circuited as shown in FIG. 14, thereby high-quality sound reproduction with the bi-wiring connection can not be realized.